Methods of pickling metals



252. COMPOSITIONS.

Patented Mar. 28, 1939 Crces 2 exam ixsmlasr UNITED STATES PATENT OFFICE METHODS OF PICKLING METALS Br' i Albert Jean Ducamp and Marie Emile Alfred Banle, Chaville, France No Drawing.

rial 1935 10 Claims.

The present invention relates to methods and compositions for pickling metals, that is to say removing superficial impurities, including oxides, from the surface of said metals.

In many industrial applications (such for instance as the application of fatty varnishes upon metals, welds, etc.) the known methods of pickling in an aqueous medium have many drawbacks: preliminary removal of grease, attack of the metallic parts that are not oxidized, necessity of rinsing with water after the treatment and of drying very carefully so as to avoid a new oxidation of the surfaces that have been pickled, all this to finally come back to the necessary fat medium for applying fatty varnishes or some welds.

It was already suggested to perform the pickling operation in a fatty medium by means of certain aliphatic acids or the like, such as stearic acid, abietic acid, etc. These methods have proved unsatisfactory, especially when it is desired to free ferrous metals from the FeaOa oxide.

The action of these acids is not suificiently strong and the metallic soaps that are formed by the combination of these acids with the metallic oxides are little soluble in fatty bodies. They rapidly form an insulating layer upon the metallic surfaces which stops the pickling operation.

On the other hand, it is a known fact that, with the pickling agents known up to the present time, the products of the combination of the metallic oxides remain in suspension or insolution in the pickling bath, thus modifying its composition, gradually reducing its efficiency and making it impossible to regenerate it after a certain time of use. It is then necessary to get rid of the whole of the bath, which is then useless, which constitutes a rather delicate problem in the case of large baths and involves heavy expenses, for instance for establishing a new bath.

The object of the present invention is to provide a pickling method and composition of matter which obviates these drawbacks.

According to the present invention, in order to efliciently and economically pickle iron, copper, their alloys, and also other metals, we treat their surface by means of a liquid having, in addition to the chemical properties necessary for dissolving metallic oxides, that of constituting a medium which is miscible neither with the water which necessarily accompanies the combination of these oxides with the acids, nor with the various waste products of this reaction, this medium being of relatively low density so that said water and said waste products spontaneously separate, due to the difference in the specific weights, from the medium in which they are produced.

This automatic separation first permits a higher efllciency of the pickling liquid owing to the liquid circulation that takes place along the sur- Application December 8, 1936, Se- No. 114,871. In France December 10,

face of the piece. On the other hand, it will be easier to maintain the pickling liquid to the desired composition. This results from the fact that the aqueous liquid resulting from this separation can be decanted without difliculty, and, g as its volume is proportional to the consumption of active-product, it will sufllce, in order to regenerate the pickling liquid, to replace the decanted portion by a substantially equal volume of a suitable regenerating liquid, containing a suit- 10 able percentage of the consumed products.

It is thus possible to make use of a pickling bath, if not indefinitely, as least for a very long time.

' We may even apply the method in a thorough- 15 ly continuous manner when it is desired to pickle pieces on an industrial scale, with a constant and regular output. In this case, according to the present invention. it will sufilce to provide means for permanently evacuating the waste products of the reaction from the lower part of the bath, whereas the corresponding amount of regenerating v liquid is also fed in a permanent manner to the bath.

The pickling liquid necessary to the'application of the method thus defined may be given various compositions and it may be used either in the cold or in the hot state".

It is, for instance, possible to constitute this liquid of alcohols or of phenols or of saturated w or unsaturated aliphatic acids or hydrocarbons or mixtures of the same, either in the presence of glycerides or not, and of one or several stronger acids capable of dissolving in these alcohols or these phenols, such as hydrochloric acid, acetic acid, phosphoric acid, formic acid, lactic acid, oxalic acid, etc.

As alcohols, we may employ, either alone or in, I mixture, methyl, ethyl, amyl, butyl alcohols and I their higher homologues, and also glycols and f their etherlfled and esterifled derivatives, these alcohols or glycols containing, or not, a small amount of trioxymethylene. We may also make use of industrial mixtures of alcohols.

As phenols, we may make use of hydroxybenzene, methylhydroxybenzenes, and their higher homologues. J 7

As fatty acids, we may make use of undecylenic acid, oleic, stearic acids, and the like.

Under the action of this bath, the metallic oxides of the surface to be pickled combine with the strong acids, yielding metallic compounds in an aqueous medium which possess the property of separating spontaneously by difference of density of the fatty medium in which they are formed.

It is easy, under these conditions, to separatev the residues from the main partif the bath and to regenerate the latter by addition of a weight of active substances equal to the weight of these m AWWlM/"lkm substances which is present in combination in the part that is removed, the regenerating liquid thus utilized being of a composition and degree of acidity different from those of the initial liquid.

We found that good pickling action can be obtained by making use, preferably in the hot state, of a mixture of an alcohol, undecylenic acid, and one or several stronger acids capable of dissolving in an alcohol, such as hydrochloric, acetic or phosphoric acid, in such manner that the metallic oxides of the surface that is treated combine with said acids and give rise to the formation of metallic complex compounds soluble in oily matters, which dissolve in the excess of fatty acid and of alcohol, the latter belonging to the group including anhydrous ethyl alcohol, butanol, glycol and its derivatives: methyl-glycol, ethyl-glycol, poly-glycol, said acidified alcohols containing or not small amounts of trioxymethylene in the dissolved state. For instance, if it is desired to pickle, according to the invention, a steel sheet covered with FeaOi oxide, either rusted or not, this sheet is immersed into a mixture containing: one part and a half of undecylenic acid, one part and a half of hydrochloric acid, and seven parts of butanol, by heating to a temperature of about 80 C., the proportions above indicated being given in volumes.

It sufilces, after CcHe, or a mixture of gasoline and anhydrous alcohol for instance, .so as to remove the last traces of iron oxide which have taken the form of complex compounds soluble in oil. The metal sheet, after treatment, is perfectly capable of receiving a fatty varnish, either in the cold state, or in an oven, or of being protected or welded in any suitable manner in an anhydrous medium.

According to the invention, the proportions of undecylenic acid and of the other acids soluble in the alcohols may vary, saine as those of the solvents.

' tom of the both.

If it is desired that the pickling mixture should attack only the oxides, without exerting any action on the metal proper, according to the invention, we dissolve in the hot state in said pickling mixture a small amount of trionmethylene, for instance from 3 per thousand to 3 per cent, and the pieces to be pickled are heated only to a temperature of 60 C.

It may be assumed that, in the hot state, in the presence of an acid mixture according to the present invention, trionmethylene produces esters which are attacked by the metallic oxides, with regeneration of the trioxymethylene and formation of metallic salts. while of course the pure metal is notcapable of attacking said esters.

We will now proceed to give some specific examples of mixtures according to the present invention.

We may for instance bath consisting of make use of an initial Per cent Undecylenic acid ......2.... 10 Anhydrous acetic acid. 5 Hydrochloric acid in aqueous solution (22 Be.) l5 Butanol '10 If an iron sheet covered with m ersed small aqueous droplets are formed stains and they drop to the botdriving along, together with them, the iron salts,and the waste products of the reaction.

At ordinary temperature, the pickling action in this ba h. under the oxide that, to wash with benzene is finished after 5 or 6 hours. At a temperature of 65 0., the operation is finished after only minutes.

If the metallic piece is allowed to stand in the bath after the oxides have disappeared, the attack on the metal is negligible.

After the operation, the aqueous liquid present at the bottom of the bathis removed, same as the residues driven along, and it is possible to regenerate the bath by replacing the part that has been removed by a substantially equal volume of the following composition:

Per cent Undecylenic acid l5 Acetic acid--- 10 Hydrochloric acid 65 Butanol, 10

preservation by protecting them against a new oxidation.

For the application of phosphatation or metallization, or other protecting coatings, it will be often necessary toremove the whole of the grease from the pieces through one of the known industrial methods. 4

Of course, it is possible, without departing from the principle of the present invention, to apply the pickling product above described in any other way than in the form of a bath, for instance for replacing sanding. By way of example, this product may be employed by atomizing, coating, or again, mixed with an inert powdery product, in the form of a paste which may adhere for the desired time on the surfaces to be pickled. In the latter case, regeneration of the product will not be possible, but the spontaneous separation of the products of the reaction will have for its eifect to create a kind of local circulation in' all points of the surface, which circulation increases the emciency of the pickling acids.

What we claim is:

1. A method for removing superficial impurities from metals, which comprises contacting said metals with a liquid water-repellent pickling composition which is a non-solvent for pickling residues and has a lower specific gravity than water.

2. A method for removing superficial impurities from metals, which comprises contacting .said

metals with a bath of a liquid, water-repellent pickling composition which is a non-solvent for pickling residues and has a lower specific gravity than water, to precipitate water togetherwith regenerating the bath is substantially immiscible with water.

a lower layer; withdraw-.

252. COMPOSITIONS.

was A cl'Ooo alum oil- 1" Examaer 1x6 I the group consisting of butanol and its higher liquid homologues.

6. A water-repellent pickling composition including hydrochloric acid, undecylenic acid and butanol.

7. A water-repellent pickling composition which includes a pickling acid selected from the group consisting of hydrochloric acid, acetic acid, phosphoric acid, formic acid, lactic acid and oxalic acid, a higher aliphatic acid, an alcohol which is substantially immiscible with water, and a small proportion of trioxymethylene. I

8. A water-repellent pickling composition including about 1.5 parts by volume of undecylenic acid, 1.5 parts by volume of hydrochloric acid and 7 parts by volume of butanol.

9. A water-repellent pickling composition which includes a pickling acid selected from the group consisting of hydrochloric acid, acetic acid, phosphoric acid, formic acid, lactic acid and oxalic acid, a higher aliphatic acid and a liquid phenol substantially immiscible with water.

10. A method for removing impurities from metal surfaces, which comprises subjecting the surfaces to the action of a water-repellent pickling composition including an acid pickling agent selected from the group consisting of hydrochloric acid, acetic acid, phosphoric acid, formic acid, lactic acid and oxalic acid, a higher aliphatic acid and a liquid phenol substantially immiscible with 20 water.

ALBERT JEAN DUCAMP. MARIE m/KLE ALFRED BAULE. 

